Did more testing this afternoon, here is another update,
I think I've ruled out the following factors:
- Not an amp issue, tried with 2 amps
- Not a RCA cable issue, I tried with 2 sets of RCA cables
- Not a ground issue - tried 4 ground points
- Not a speaker/tweeter issue. 2 reasons, first I can hear hissing noise distinctively from
both when gain is turned up, 2nd the noise is gone with unplug the HU or replace it with another source ipod
What is left
- HU noise. but this is unlikely, because it wasn't there before.
- Harness connection related problem, it is creating some sort of feedback or harsh connection? Not sure how to test this, any idea? Should I try with another harness?
- Lastly do you think a MS8 equalizer would help with this problem?